One need for purified protein is derived from the pharmaceutical industry's interest in protein products as therapeutic agents. Protein therapeutic agents can be used in humans against any number of diseases, including cancer, immunodeficiency diseases and various types of infections. However, since many medicinal proteins are prepared from genetically engineered bacteria, procaryotic protein impurities can present costly problems in final purification steps. It is essential to remove these contaminants because they are immunogenic. If the contaminants are allergenic, even minute amounts can cause significant adverse side reactions. Accordingly, protein therapeutic agents must be extremely pure.
Over the past ten years there has been an exponential growth in protein pharmaceuticals. Human insulin, interferons, human growth hormone, TPA (tissue plasminogen activator) and erythropoietin are examples. This is so mainly because of genetic engineering techniques which allow for the large scale microorganism synthesis of proteins that occur in minute amounts in the human body.
It is known to grow protein crystals in microgravity using hanging drops in a vapor diffusion apparatus (VDA). However, the disadvantage of this method is that it produces limited amounts of crystals because the volume of the hanging drop is small, i.e., 0.05 mL. The yield is sufficient to supply research amounts of the protein crystals for x-ray crystallography, but cannot be considered a large scale method that could provide bulk amounts of protein crystals. Another limitation of the hanging drop method, which again is due to the small sample size, is the problem of droplet surface effects. Flow patterns on the surface may adversely affect protein crystal growth.